Method for determining the speed variation between wheels of different axles of a vehicle

Abstract

An improved method is used to determine speed variation between wheels of different axles of a vehicle. The difference between the speeds of the rear wheels and the speeds of the front wheels is formed, and a correction is determined which compensates for the variations between the speeds of the front wheels and the rear wheels arising because of the vehicle geometry. The speed variation between the wheels of different axles of a vehicle is given by the difference plus the correction and, under particular driving conditions, which are characterized at least in that the acceleration of the rear wheels is below a threshold value at which there is no speed difference between the wheels of different axles because of drive slip, an adaptation of the correction takes place by determining the difference between the speeds of the rear wheels and the front wheels and by adapting the correction in such a way that the correction, under the particular driving conditions, is equal with respect to magnitude to the difference between the speeds of the rear wheels and the front wheels and exhibits a change of sign relative to this difference. In addition, or alternatively, in determining the correction, the vehicle transverse acceleration is taken into account by the magnitude of the correction becoming smaller with increasing transverse acceleration.

We claim: 
     
       1. A method for determining speed variation between driven and undriven wheels of vehicle axles, comprising the steps of sensing speeds of front and rear vehicle wheels,   forming a difference between the speeds of the rear wheels and of the front wheels,   determining a correction factor which compensates for the variations between the speeds of the front wheels and the rear wheels arising from vehicle geometry, and   providing to a vehicle system the speed variation between the speed of driven and undriven vehicle axles in terms of the difference plus the correction factor,   wherein, in the step of determining the correction factor, vehicle dynamics are taken into account by reducing a magnitude of the correction factor with increasing transverse acceleration.   
     
     
       2. The method according to claim 1, wherein a difference represented by DV is determined from the following equation:   DV=VHM-VVM+h(VVM)*f(DLR)*VVM,     where VHM and VVM represent the speeds of the rear wheels and the front wheels, respectively DLR represents the difference between the front-wheel speeds referred to the average front-wheel speed VVM and an improvement function represented by h(VVM) tends asymptotically to zero so that the correction represented by h(VVM),f(DLR),VVM also tends asymptotically to zero.   
     
     
       3. The method according to claim 2, wherein under particular driving conditions characterized at least in that acceleration of the rear wheels is below a threshold value and the vehicle is travelling around a curve, such that the speed difference of the wheels of the separate vehicle axles due to drive/slip does not exist, an adaptation of the correction takes place in which values of a model function are stored at particular interpolation points, the model function being a function averaged from the improvement function determined for individual vehicle types, and the adaptation of the correction function initially takes place at lower front wheel speeds and in which, at the interpolation points of the value of the front wheel speeds, at which the value of the model function is stored, the value of the improvement function is then determined such that the correction is equal in magnitude to the difference, the sign of the correction being reverse to the sign of the difference and the specific value of the improvement function. 
     
     
       4. The method according to claim 2, wherein under particular driving conditions characterized at least in that the acceleration of the rear wheels is below a threshold value and the vehicle is travelling around a curve such that a speed difference of the wheels of the separate vehicle axles due to drive slip does not exist, an adaptation of the correction takes place in which values of a model function are stored at particular interpolation points, the model function being a function averaged from improvement functions determined for individual vehicle types, and the adaptation of the correction function initially takes place at lower front wheel speeds and an adaptation of the improvement function then takes place in which, at one interpolation point of the value of the front wheel speeds at which the value of the model function is stored, a factor is determined such that the value of the model function at this interpolation point multiplied by the factor gives a value of the improvement function such that the correction is equal in magnitude to the difference, the sign of the correction being the reverse to the sign of the difference and the adapted values of the improvement function at the other interpolation points VVM being obtained by multiplying the values of the model function at the other interpolation points by the factor. 
     
     
       5. A method for determining speed variation between driven and undriven wheels of vehicle axles, comprising the steps of sensing speeds of front and rear vehicle wheels,   forming a difference between the sensed speeds of the rear wheels and of front wheels,   determining a correction factor which compensates for the variations between the speeds of the front wheels and the rear wheels arising from vehicle geometry, and   providing to a vehicle system the speed variation between the wheels of the vehicle axles in terms of the difference plus the correction factor,   wherein, under particular driving conditions in which acceleration of the driven wheels is below a threshold value and that the vehicle is travelling around a curve to produce transverse vehicle acceleration such that no speed difference of the wheels of separate vehicle axles due to drive slip exists, the correction arising from vehicle geometry is modified inversely to an increase in the transverse vehicle acceleration arising from vehicle dynamics, and wherein the correction as modified exhibits a change of sign relative to the difference.   
     
     
       6. The method according to claim 5, wherein the step of determining the difference represented as DV is based on the following equation:   DV=VHM-VVM+f(DLR)*VVM,     where VHM is the speed of the rear wheels, DLR is a difference between the front-wheel speeds referred to the average front-wheel speed represented by VVM, values of a model function represented by f(DLR) model  are stored at particular interpolation points represented by DLR, the model function f(DLR) model  being a function averaged from correction functions represented by f(DLR) determined for individual vehicle types, and the adaptation of the correction takes place by an adaptation of the correction function f(DLR) in which the value of the correction function f(DLR) is determined, at the interpolation points of the value DLR at which the value of the model function f(DLR) model  is stored, such that the correction represented by f(DLR)*VVM is equal with respect to magnitude to the difference VHM-VVM, the sign of the correction being reverse to the sign of the difference and the particular value of the correction function f(DLR) being the adapted value of the model function f(DLR) model .   
     
     
       7. The method according to claim 5, wherein the step of determining the difference represented by DV is based on the following equation:   DV=VHM-VVM+f(DLR)*VVM,     where VHM is the speed of the rear wheels, DLR is the difference between the front-wheel speeds referred to the average front-wheel speed represented by VVM, in that values of a model function represented by f(DLR) model  are stored at particular interpolation points represented by DLR, the model function f(DLR) model  being a function averaged from correction functions f(DLR) determined for individual vehicle types, and the adaptation of the correction takes place by an adaptation of the correction function f(DLR) in which a factor is determined, at one interpolation point of the value DLR at which the value of the model function f(DLR) model  is stored, such that the value of the model function f(DLR) model  at this interpolation point multiplied by the factor gives a value of the correction function f(DLR) such that the correction represented by f(DLR)*VVM is equal with respect to magnitude to the difference VHM-VVM, the sign of the correction being reverse to the sign of the difference and the adapted values of the correction function f(DLR) at the other interpolation points DLR being obtained by multiplying the values of the model function f(DLR) model  at the other interpolation points by the factor.   
     
     
       8. The method according to claim 5, wherein the particular driving conditions includes at least one of the following conditions: (a) a vehicle engine is running,   (b) a braking procedure is not taking place,   (c) vehicle speed is within a particular speed range,   (d) vehicle transverse acceleration is below a particular threshold value, and   (e) a variation between the speeds of the rear wheels and the front wheels is below a threshold value.   
     
     
       9. The method according to claim 8, wherein the step of determining the difference represented as DV is based on the following equation:   DV=VHM-VVM+f(DLR)*VVM,     where VHM is the speed of the rear wheels, DLR is a difference between the front-wheel speeds referred to the average front-wheel speed represented by VVM, values of a model function represented by f(DLR) model  are stored at particular interpolation points represented by DLR, the model function f(DLR) model  being a function averaged from correction functions represented by f(DLR) determined for individual vehicle types, and the adaptation of the correction takes place by an adaptation of the correction function f(DLR) in which the value of the correction function f(DLR) is determined, at the interpolation points of the value DLR at which the value of the model function f(DLR) model  is stored, such that the correction represented by f(DLR)*VVM is equal with respect to magnitude to the difference VHM-VVM, the sign of the correction being reverse to the sign of the difference and the particular value of the correction function f(DLR) being the adapted value of the model function f(DLR) model .   
     
     
       10. The method according to claim 8, wherein the step of determining the difference represented by DV is based on the following equation:   DV=VHM-VVM+f(DLR)*VVM,     where VHM is the speed of the rear wheels, DLR is a difference between the front-wheel speeds referred to the average front-wheel speed represented by VVM, in that values of a model function represented by f(DLR) model  are stored at particular interpolation points represented by DLR, the model function f(DLR) model  being a function averaged from correction functions f(DLR) determined for individual vehicle types, and the adaptation of the correction takes place by an adaptation of the correction function f(DLR) in which a factor is determined, at one interpolation point of the value DLR at which the value of the model function f(DLR) model  is stored, such that the value of the model function f(DLR) model  at this interpolation point multiplied by the factor gives a value of the correction function f(DLR) such that the correction represented by f(DLR)*VVM is equal with respect to magnitude to the difference VHM-VVM, the sign of the correction being reverse to the sign of the difference and the adapted values of the correction function f(DLR) at the other interpolation points DLR being obtained by multiplying the values of the model function f(DLR) model  at the other interpolation points by the factor.   
     
     
       11. The method according to claim 8, wherein a difference represented by DV is determined from the following equation:   DV=VHM-VVM+h(VVM)*f(DLR)*VVM,     where VHM and VVM represent the speeds of the rear wheels and the front wheels, respectively DLR represents the difference between the front-wheel speeds referred to the average front-wheel speed VVM and an improvement function represented by h(VVM) tends asymptotically to zero so that the correction represented by h(VVM)*f(DLR)*VVM also tends asymptotically to zero.   
     
     
       12. The method according to claim 11, wherein under particular driving conditions characterized at least in that acceleration of the rear wheels is below a threshold value and the vehicle is travelling around a curve, such that the speed difference of the wheels of the separate vehicle axles due to drive/slip does not exist, an adaptation of the correction takes place in which values of a model function are stored at particular interpolation points, the model function being a function averaged from the improvement function determined for individual vehicle types, and the adaptation of the correction function initially takes place at lower front wheel speeds and in which, at the interpolation points of the value of the front wheel speeds, at which the value of the model function is stored, the value of the improvement function is then determined such that the correction is equal in magnitude to the difference, the sign of the correction being reverse to the sign of the difference and the specific value of the improvement function. 
     
     
       13. The method according to claim 11, wherein under particular driving conditions characterized at least in that the acceleration of the rear wheels is below a threshold value and the vehicle is travelling around a curve such that a speed difference of the wheels of the separate vehicle axles due to drive slip does not exist, an adaptation of the correction takes place in which values of a model function are stored at particular interpolation points, the model function being a function averaged from improvement functions determined for individual vehicle types, and the adaptation of the correction function initially takes place at lower front wheel speeds and an adaptation of the improvement function then takes place in which, at one interpolation point of the value of the front wheel speeds at which the value of the model function is stored, a factor is determined such that the value of the model function at this interpolation point multiplied by the factor gives a value of the improvement function such that the correction is equal in magnitude to the difference, the sign of the correction being the reverse to the sign of the difference and the adapted values of the improvement function at the other interpolation points VVM being obtained by multiplying the values of the model function at the other interpolation points by the factor.